Systems and methods for testing packaged microelectronic devices

ABSTRACT

Systems and methods for testing packaged microelectronic devices are disclosed herein. One such system for testing a packaged microelectronic device includes a test socket configured to receive the device for testing and a tester interface including a plurality of test contacts aligned with external contacts of the device when the device is received within the test socket. The system further includes a mask proximate to the test socket and the test contacts. The mask includes a plurality of apertures arranged in a pattern corresponding to the plurality of test contacts and corresponding at least in part to the array of external contacts when the device is received within the test socket. The apertures include (a) first apertures sized to allow the corresponding test contacts to extend completely through the mask, and (b) one or more second apertures sized to allow the corresponding test contacts to extend only partially through the mask.

TECHNICAL FIELD

The present disclosure is directed generally toward systems and methodsfor testing packaged microelectronic devices.

BACKGROUND

Conventional packaged microelectronic devices are manufactured forspecific performance characteristics required for use in a wide range ofelectronic equipment. Packaged microelectronic devices typically includea die with integrated circuitry, a casing encapsulating the die, and anarray of external contacts or terminals. Packaged microelectronicdevices have an outer shape that defines a package profile. The externalcontacts can include (a) contacts that protrude from the device (e.g.,pin-like leads, ball-pads, solder balls, or bumps of a ball-grid array(BGA), etc.) or (b) non-protruding, generally planar contacts or pads(e.g., land grid arrays (LGA), leadless chip carriers, quad flat-packno-lead packages, etc.) The external contacts are arranged in a selectedpattern and configured to be electrically and physically coupled toother external devices. Different types of packaged devices withdifferent circuitry can have the same outer profile but a differentarrangement of external contacts.

After the dies are packaged, the devices are generally tested and markedin several post-production batch processes. Burn-in testing is one suchpost-production process for detecting whether any of the devices arelikely to fail. Burn-in testing is performed before shipping packageddevices to customers or installing packaged devices in electronicequipment. Burn-in testing of packaged devices typically involvesapplying specified electrical biases and/or signals to the externalcontacts of the devices in a controlled temperature environment. Thepackaged devices are generally tested under more severe conditionsand/or under more rigorous performance parameters than they are likelyto experience during normal operation.

FIG. 1, for example, is a schematic side cross-sectional view of aportion of a conventional testing system 10 including a test bed 20carrying a packaged microelectronic device 12. The test bed 20 includesa test socket 22 having lead-in surfaces 24 and side surfaces 26 thatdefine a recess 28 for receiving the device 12. A shelf 30 in the recess28 supports an outer perimeter region of the device 12, and externalcontacts 14 on the device 12 are positioned within an opening 32 definedby the shelf 30. A tester interface 40 that includes a plurality of testcontacts 42 is positioned below the test bed 20 with the test contacts42 positioned to contact corresponding external contacts 14.

The test contacts 42 can be selected based on the particularconfiguration of the external contacts 14. For example, if the externalcontacts 14 include protruding elements such as solder balls, the testcontacts 42 can include clamps or pincers configured to pinch or holdthe protruding contacts 14. On the other hand, if the external contacts14 include generally planar elements, such as an LGA, the test contacts42 can include vertically biased contacts configured to engage thecorresponding non-protruding contacts 14. The test socket 22 is movablerelative to the tester interface 40 so that the test contacts 42 canengage and apply electrical signals to corresponding external contacts14 for testing the device 12. Although only a single test socket 22 anddevice 12 are shown in FIG. 1, it will be appreciated that the system 10can include a number of test sockets 22 for testing a number of devices12 either individually or in a batch process.

One problem with conventional testing systems is that it is difficult toperform burn-in tests for runs of devices having differentconfigurations. For example, the arrangement of external contacts on onebatch of devices to be tested may be different than the arrangement ofexternal contacts on another batch of devices and, accordingly, theexternal contacts of the individual devices may not be aligned withcorresponding test contacts. In the testing system 10 of FIG. 1, forexample, the arrangement of test contacts 42 may not be the same as thearrangement of external contacts 14 on the device 12. As such, theexternal contacts 14 may not be properly aligned with the test contacts42 and the device 12 may fail the test even though the device 12otherwise functions properly. Furthermore, if one or more portions ofthe device 12 are not populated with external contacts 14, the testcontact(s) 42 aligned with that portion of the device 12 can scratch,impinge, pierce, and/or otherwise damage the device 12. In some cases,for example, the unmatched test contacts 42 can puncture the soft,protective coating on an external surface of the device 12 and damage orshort out the device's internal circuitry.

One approach to addressing this drawback is to reconfigure the testingsystem to accommodate the different arrangements of external contacts oneach device to be tested. In the testing system 10 of FIG. 1, forexample, the system can be reconfigured by replacing the test sockets 22with different test sockets configured for use with a particular batchof devices. Further, in some cases the tester interface 40 can bereconfigured by adding or eliminating test contacts 42 such that thenumber and arrangement of test contacts 42 is precisely coordinated withthe arrangement of external contacts 14 on the device 12. In a typicallarge scale manufacturing process for microelectronic devices, however,replacing each of the test sockets 22 and/or reconfiguring the testcontacts 42 to test devices having different arrangements of externalcontacts typically involves reconfiguring a large number of systemcomponents. This process is accordingly extremely labor-intensive,time-consuming, and expensive because it not only requires many hours ofskilled labor, but it also results in costly downtime for the testingsystems. Accordingly, there is a need for improved systems and methodsfor testing microelectronic devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side cross-sectional view of a portion of a systemfor testing microelectronic devices in accordance with the prior art.

FIG. 2 is a schematic side cross-sectional view of a system for testinga plurality of microelectronic devices in accordance with one embodimentof the invention.

FIG. 3A is an isometric view including a cut-out portion of one of thetest sockets of FIG. 2.

FIG. 3B is a side cross-sectional view of the test socket of FIG. 3Ataken substantially along the line 3B-3B.

FIGS. 4A and 4B are enlarged views of a portion of the test socket shownin FIG. 3B.

FIG. 5 is a side cross-sectional view of a test socket configured inaccordance with another embodiment of the invention.

FIG. 6 is a side cross-sectional view of a portion of a test socketconfigured in accordance with still another embodiment of the invention.

DETAILED DESCRIPTION

The following disclosure describes several embodiments of systems andmethods for testing packaged microelectronic devices. The term“microelectronic device” is used throughout to include semiconductordevices, microfeature devices, micromechanical devices, optics, datastorage elements, read/write components, and other articles ofmanufacture. For example, microelectronic devices can include imagers,SRAM, DRAM (e.g., DDR-SDRAM), flash memory (e.g., NAND flash memory),ASICS, processors, flip chips, LGA chips, ball-grid array chips, andother types of microelectronic devices or components. Several specificdetails of the invention are set forth in the following description andin FIGS. 2-6 to provide a thorough understanding of certain embodimentsof the invention. A person skilled in the relevant art will understand,however, that the invention has additional embodiments, and that theinvention may be practiced without several of the specific featuresdescribed below.

FIG. 2 is a schematic side cross-sectional view of a system 100 fortesting a plurality of packaged microelectronic devices 102 inaccordance with one embodiment of the invention. Each device 102includes a substrate 104, integrated circuitry (not shown), and aplurality of external contacts or pads 106 arranged in a desired arrayon the substrate 104. In the illustrated embodiment, for example, thecontacts 106 are arranged in an LGA. In other embodiments, however, thedevices 102 can have other configurations and/or can include other typesof semiconductor components. The system 100 can test the devices 102individually or in a batch process to ensure and verify that the devices102 function according to specification.

The illustrated system 100 includes a test tray 110 and a plurality oftest sockets 120 carried by the test tray 110. The individual testsockets 120 include (a) a nesting portion 122 configured to carrycorresponding devices 102, and (b) a base portion 124 configured tosupport the nesting portion 122. The system 100 also includes a testerinterface 150 having a plurality of test contacts or electricalinterconnect elements 152 arranged in an array corresponding at least inpart to the external contacts 106 on the individual devices 102. Theillustrated test contacts 152 include vertically activated spring-typecontacts. In other embodiments, however, the test contacts 152 caninclude other types of contacts or interconnect elements. The testsockets 120 and/or the test contacts 152 are movable relative to eachother so that the test contacts 152 can selectively contact and applyelectrical signals to external contacts 106 and test the devices 102.The system 100 also includes a controller 154 operatively coupled to thetester interface 150. The controller 154 sends/receives signals from thedevices 102 via the tester interface 150.

The system 100 further includes a mask 130 between the individualdevices 102 within each test socket 120 and the corresponding testcontacts 152. In the illustrated embodiment, the masks 130 are anintegral component of the nesting portions 122 of each test socket 120.In other embodiments, however, the masks 130 can be separate componentsremovably installed with each test socket 120. The individual masks 130each include a plurality of apertures 132 arranged in a patterncorresponding to the particular arrangement of test contacts 152 andalso corresponding at least in part to the array of external contacts106 on the devices 102. More specifically, each mask 130 includes anumber of apertures 132 configured to allow corresponding test contacts152 to extend completely through the mask and contact the externalcontacts 106, and one or more additional apertures configured to preventthe corresponding test contacts from extending completely through themask such that the test contacts 152 do not engage the correspondingdevices 102. Further details regarding the test sockets 120 and masks130 are described below with reference to FIGS. 3A-6.

FIG. 3A, for example, is an isometric view including a cut-out portionof one of the test sockets 120 of FIG. 2. FIG. 3B is a sidecross-sectional view of the test socket 120 of FIG. 3A takensubstantially along the line 3B-3B. Each of these Figures has beengreatly simplified to illustrate only particular aspects of the testsocket 120 and, accordingly, a number of components associated with thetest socket 120 are not shown. For example, a socket lid and a forcedistribution member (e.g., a pusher assembly) are not illustrated toavoid obscuring particular aspects of the test socket 120.

Referring to FIGS. 3A and 3B together, the nesting portion 122 of theillustrated test socket 120 includes a body 124 having a plurality oflead-in surfaces 126, a plurality of side surfaces 128 connected tocorresponding lead-in surfaces 126, and the mask 130 extending betweenthe side surfaces 128. The lead-in surfaces 126, side surfaces 128, andmask 130 define a recess 129 for receiving one of the devices 102. Therecess 129 is shaped to closely correspond to the outer profile or shapeof the device 102. For example, the lead-in surfaces 126 taper inwardlyfrom a top surface 125 of the body 124 to the side surfaces 128 tocontrol the position of the device 102 within the test socket 120 inthree dimensions (e.g., the x, y, and z axes) such that the device 102is precisely positioned in the test socket 120. In other embodiments,the body 124 can have other configurations that may not include fourlead-in surfaces 126 and/or four side surfaces 128. For example, thebody 124 can include one tapered lead-in surface extending from the topsurface 125 to the mask 130 and three non-tapered side surfacesextending from the top surface 125 to the mask 130. In otherembodiments, the body 124 can have a number of other arrangements and/orconfigurations.

The base portion 140 of the test socket 120 includes a body 142 and aplurality of side surfaces 144 that define an opening 146 through whichthe test contacts 152 extend between the tester interface 150 (FIG. 2)and the mask 130. As discussed previously, the base portion 140 isconfigured to carry or otherwise support the nesting portion 122. In theillustrated embodiment, for example, the nesting portion 122 is spacedapart or otherwise suspended above the base portion 140 by a gap G.During a testing operation, the nesting portion 122 is moved relative tothe base portion 140 to bring the two portions into contact and bringthe test contacts 152 into contact with corresponding external contacts106 to test the device 102. The base portion 140 further includes one ormore alignment features 148 (FIG. 3B) to properly position the testsocket 120 relative to the test bed 110 (FIG. 2). In the illustratedembodiment, for example, the alignment feature 148 is a pin that mateswith a corresponding aperture in the test bed 110 (FIG. 2) to preciselyalign the test socket 120.

The mask 130 includes a first surface or support surface 134 facing thedevice 102 and a second surface or an exterior surface 135 opposite thesupport surface 134. The apertures 132 extend through the mask 130 fromthe support surface 134 to the exterior surface 135. In the illustratedembodiment, the mask 130 is an integral component of the nesting portion122. In other embodiments, however, such as the embodiment discussedbelow with reference to FIG. 5, the mask can be a separate componentfrom the nesting portion 122. As discussed previously, the apertures 132are arranged in an array corresponding at least in part to the array ofexternal contacts 106 on the device 102. More specifically, theapertures 132 are configured to selectively allow certain test contacts152 to contact corresponding external contacts 106, while blocking orotherwise restricting other test contacts 152 from contacting the device102. Further details regarding the apertures 132 and the test elements152 are discussed below with reference to FIGS. 4A and 4B.

FIGS. 4A and 4B are enlarged views of an area 4A shown in FIG. 3B.Referring first to FIG. 4A, the size, position, and configuration of theapertures 132 through the mask 130 correspond with the arrangement ofexternal contacts 106 on the device 102. In the illustrated embodiment,for example, the mask 130 includes first apertures 132 a aligned with atleast some of the external contacts 106, and second apertures 132 baligned with unpopulated portions of the device 102 (e.g., aperturesthat are not aligned with any of the external contacts 106). The firstapertures 132 a have a first diameter or cross-sectional dimension D₁and the second apertures 132 b have a second diameter or cross-sectionaldimension D₂ less than the first diameter D₁.

Individual test contacts 152 are aligned with each of the first andsecond apertures 132 a and 132 b, and at least a portion of each testcontact 152 extends into the corresponding aperture. More specifically,the test contacts 152 each include a body portion 154, an engagement ortip portion 156 extending from the body portion 154 into at least aportion of the individual apertures 132, and a shoulder 158 between thebody portion 154 and the engagement portion 156. The shoulder 158 can bea rim or other lateral element extending transversely with respect tothe body portion 154 and the engagement portion 156. Each body portion154 has a third diameter or cross-sectional dimension D₃ greater thanthe second diameter D₂, but less than the first diameter D₁. Eachengagement portion 156 has a fourth diameter or cross-sectionaldimension D₄ less than the first, second, and third diameters D₁, D₂,and D₃, respectively.

Referring next to FIG. 4B, a force (as shown by the arrow A) is appliedto the device 102 and/or the nesting portion 122 (FIG. 3B) to move thedevice 102 relative to the test contacts 152. As the force F moves thedevice 102 downward, selected test contacts 152 contact the externalcontacts 106 for testing, while other test contacts 152 are blocked orotherwise restricted from contacting the device 102. More specifically,the device 102 and the mask 130 move relative to the test contacts 152until the exterior surface 135 of the mask 130 contacts the body 142 ofthe base portion 140 (FIG. 3B). This downward movement of the mask 130accordingly urges the device 102 and mask 130 toward the test contacts152. Because the first diameter D₁ of the first apertures 132 a isgreater than the third diameter D₃ of the body portion 154 of the testcontacts 152, the test contacts 152 can move through at least a portionof each first aperture 132 a until the engagement portions 156 contactcorresponding external contacts 106.

On the other hand, the second diameter D₂ of the second apertures 132 bis less than the third diameter D₃. Accordingly, the shoulders 158 ofthe test contacts 152 aligned with the second apertures 132 b engage theexterior surface 135 of the mask 130 proximate to the correspondingsecond apertures 132 b and prevent the engagement portions 156 frommoving completely through the second apertures 132 b into contact withthe device 102. Because the second diameter D₂ of the second apertures132 b is greater than the fourth diameter D₄ of the engagement portions156, however, the engagement portions 156 of the test contacts 152aligned with the second apertures 132 b do not make physical contactwith the mask 130. The second apertures 132 b accordingly prevent thecorresponding engagement portions 156 from physically engaging the mask130 and potentially being damaged or broken as a result of such contact.In other embodiments, the mask 130 can have a number of otherarrangements and/or configurations. Additional embodiments of masks fortest sockets are described below with reference to FIGS. 5 and 6. In anyof these embodiments, the mask can be configured to selectively allowcertain test contacts 152 to engage the device 102, while restrictingother test contacts 152 from engagement in a way that protects thedelicate and sensitive test contacts 152 from damage.

The array of apertures 132 in the mask 130 described above withreference to FIGS. 2-4B can be used to selectively control which testcontacts 152 engage the external contacts 106 on the device 102, andwhich do not. For example, the mask 130 can prevent the test contacts152 aligned with unpopulated portions of the device 102 (e.g., portionsthat do not include an external contact 106) from contacting the device102. As a result, the device substrate 104 is significantly less likelyto be contaminated and/or damaged by the test contacts 152. In someembodiments, for example, the device 102 may only have a thin, softprotective coating over its internal components. In many conventionalsockets, such as those described previously, the test contacts canengage unpopulated portions of the device and pierce or otherwise breakthrough the protective coating to damage or short out the internalcircuitry. The illustrated test socket 120 can accordingly reduce thelikelihood that the devices 102 will be damaged and/or contaminatedduring testing. Moreover, residue and/or debris from the substrate 104will not accumulate on the test contacts 152. Such residue cannegatively impact the performance of the affected test contacts 152 andpotentially cause the test contacts 152 to malfunction and/or becomeinoperable.

Embodiments of the test sockets 120 described above with reference toFIGS. 2-4B include the nesting portion 122 and integral mask 130 as amodular component that can be removed from the test socket 120 andreplaced with another nesting portion having a customized mask based onthe particular configuration of each batch of devices to be tested. As aresult, replacing the nesting portion 122 with the integral mask 130 isa relatively quick and easy process compared to the conventional systemsdescribed above in which the entire test socket 120 and/or the testerinterface 150 must be replaced or reconfigured before testing a batch ofdevices having a different configuration. Furthermore, the cost ofkeeping an inventory of nesting portions 122 with masks 130 havingdifferent configurations is less than the cost of keeping an inventoryof entire test sockets and associated hardware. The testing system 100including the test sockets 120, for example, provides a significantreduction in tooling cost as compared with testing systems usingconventional test sockets where a large number of different test socketsmust be kept on hand for testing devices having differentconfigurations.

In at least some of the embodiments of the test sockets 120 describedabove, it may be desirable to isolate one or more populated portions ofa particular device 102 during testing. Isolating selected externalcontacts 106, for example, can be used to change the particular device'sfunctionality. The mask 130 can accordingly include second apertures 132b aligned with one or more external contacts 106 to prevent thecorresponding test contacts 152 from contacting the respective externalcontacts 106 during testing. Nesting portions 120 including the integralmask 130 can make this process relatively quick and easy to accomplishand, accordingly, can facilitate a number of different testingapproaches that were too time-consuming and/or expensive withconventional testing systems.

FIG. 5 is a side cross-sectional view of a test socket 220 configured inaccordance with another embodiment of the invention. The test socket 220includes a number of features generally similar to the test socket 120described above and, accordingly, like reference numbers refer to likecomponents in FIGS. 2-3B and FIG. 5. The test socket 220 differs fromthe test socket 120 described previously in that the test socket 220 hasa nesting portion 222 with a different configuration than the nestingportion 122.

More specifically, the nesting portion 222 does not include an integralmasking portion. Rather, a mask 230 can be installed in and uninstalledfrom a body 224 of the nesting portion 222. In the illustratedembodiment, for example, the body 224 includes a shelf 227 proximate tothe base of the body 224. The mask 230 includes a referencing element234 for contacting the shelf 227 and precisely positioning the mask 230relative to the body 224. In other embodiments, however, the mask 230can be positioned within the nesting portion 222 using anotherarrangement.

The mask 230 can be generally similar to the mask 130 described above.For example, the mask 230 includes a plurality of apertures 232 arrangedin an array corresponding at least in part to the array of externalcontacts 106 on the device 102. The mask 230 can accordingly performmany of the same functions as the mask 130 described above withreference to FIGS. 2-4B. In addition, reconfiguring the test socket 220to test a batch of devices having a different configuration includesonly replacing the mask 230 with another mask having a desiredarrangement. Thus, the cost of testing multiple device types can bereduced because keeping an inventory of masks 230 having differentconfigurations is expected to be significantly less costly than keepingan inventory of larger and more complex test sockets 230.

In at least some embodiments, the mask 230 can be retrofit onto existingtest sockets, such as the socket 20 illustrated in FIG. 1, so that thetest contacts can contact and apply electrical signals to only selectedexternal contacts on the device. Accordingly, several of the drawbacksassociated with conventional test sockets described above with referenceto FIG. 1 can be overcome by using the mask 230 in conjunction withconventional test sockets.

FIG. 6 is a side cross-sectional view of a portion of a test socket 320configured in accordance with still another embodiment of the invention.More specifically, FIG. 6 illustrates a portion of the test socket 320after the force A is applied to the device 102 and/or the nestingportion (not shown) to move the device 102 relative to the test contacts152. This view of the test socket 320 and device 102 in FIG. 6 isgenerally similar to the view described above with reference to FIG. 4B.The illustrated test socket 320, however, differs from the test sockets120 and 220 described previously in that the test socket 320 has a mask330 with a different configuration than the previously-described masks130 and 230.

The mask 330, for example, includes a conductive layer 336 at anexterior surface 335 of the mask 330. The conductive layer 336 can be onand/or in the mask 330. The conductive layer 336 can include, forexample, electrically conductive plating, electrically conductive paint,one or more conductive vias extending through at least a portion of themask 330, and/or other types of suitable electrical contacts or pads.The conductive layer 336 may cover all or just a portion of the exteriorsurface 335 of the mask 330. The mask 330 also includes a supportsurface 334 opposite the exterior surface 335 and a plurality of firstapertures 332 a and second apertures 332 b extending through the mask330 from the support surface 334 to the exterior surface 335. The firstand second apertures 332 a and 332 b are generally similar to the firstand second apertures 132 a and 132 b described above. For example, thefirst apertures 332 a are arranged in an array corresponding at least inpart to the array of external contacts 106 on the device 102, while thesecond apertures 332 b are generally aligned with unpopulated portionsof the device 102. In operation, one or more of the shoulders 158 ofeach test contact 152 aligned with the second apertures 332 b can engagethe conductive layer 336 and electrically couple the respective contactto the conductive layer 336 for shorting, grounding, bridging, orotherwise electrically coupling the tester interface (not shown) to oneor more portions of the conductive layer 336. This allows the user toselectively isolate particular contacts for further diagnosis.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. For example, the test contacts caninclude a number of other types of vertically-activated electricalinterconnect elements including, but not limited to, flat springelements (e.g., stamped or chemically etched), formed spring elements,and/or other suitable types of spring probe assemblies. Further, many ofthe elements of one embodiment can be combined with other embodiments inaddition to, or in lieu of, the elements of the other embodiments.Accordingly, the invention is not limited except as by the appendedclaims.

1. A system for testing a packaged microelectronic device including an array of external contacts, the system comprising: a test socket configured to receive the device for testing; a tester interface including a plurality of test contacts aligned with external contacts of the device when the device is received within the test socket; and a mask proximate to the test socket and the test contacts, the mask including a plurality of apertures arranged in a pattern corresponding to the plurality of test contacts and corresponding at least in part to the array of external contacts when the device is received within the nesting portion, the plurality of apertures including (a) first apertures sized to allow the corresponding test contacts to extend completely through the mask, and (b) one or more second apertures sized to allow the corresponding test contacts to extend only partially through the mask.
 2. The system of claim 1 wherein the mask comprises: a first surface facing the device when the device is received within the nesting portion; a second surface opposite the first surface; and wherein the first apertures extend completely through the mask from the first surface to the second surface, the first apertures having a first cross-sectional dimension; and wherein the second apertures extend completely through the mask from the first surface to the second surface, the second apertures having a second cross-sectional dimension less than the first cross-sectional dimension.
 3. The system of claim 1 wherein: the individual test contacts include vertically arranged electrical interconnect elements having a body portion, a tip portion projecting from the body portion, and a shoulder portion between the body portion and the tip portion; the first apertures have a first cross-sectional dimension sized to receive the test contacts with at least the tip portion of each corresponding test contact extending completely through the mask; and the second apertures have a second cross-sectional dimension less than the first cross-sectional dimension, and wherein the shoulder portions of the test contacts aligned with the second apertures engage the mask and allow the tip portions of the corresponding test contacts to extend only partially through the mask.
 4. The system of claim 1 wherein: the first apertures in the mask are arranged in rows and columns corresponding to the array of external contacts on the device; and the second apertures in the mask are arranged in rows and columns corresponding to one or more portions of the device that do not include external contacts.
 5. The system of claim 1 wherein at least a portion of the second apertures are aligned with particular external contacts on the device to isolate these particular external contacts during testing.
 6. The system of claim 1 wherein the mask includes a first surface facing the device when the device is received within the nesting portion and a second surface opposite the first surface, and wherein the mask further comprises: a conductive layer positioned proximate to at least one of the second apertures, and wherein the test contacts aligned with the corresponding second apertures engage the conductive layer during testing to electrically couple the tester interface to the conductive layer.
 7. The system of claim 1 wherein the mask is an integral component of the test socket.
 8. The system of claim 1 wherein the mask is a separate component from the test socket, and wherein the mask is releasably received by the test socket before the device is received within the test socket.
 9. The system of claim 1 wherein: the test socket includes a body having one or more lead-in surfaces and a plurality of side surfaces connected to corresponding lead-in surfaces; and the mask is an integral component of the body and extends between the side surfaces with the one or more lead-in surfaces, the side surfaces, and the mask at least partially defining a recess for receiving the device.
 10. The system of claim 1 wherein: the test socket includes a body having one or more lead-in surfaces and a plurality of side surfaces connected to corresponding lead-in surfaces; and the mask is releasably received by the nesting portion between the side surfaces with the one or more lead-in surfaces, the side surfaces, and the installed mask at least partially defining a recess for receiving the device.
 11. The system of claim 1, further comprising the packaged microelectronic device.
 12. The system of claim 11 wherein the external contacts of the device are generally planar, non-protruding external contacts.
 13. The system of claim 11 wherein the external contacts are arranged in a land grid array.
 14. The system of claim 11 wherein the packaged microelectronic device is a first device having a first array of external contacts and the mask is a first mask having a plurality of apertures arranged in a first pattern, and wherein the system further comprises: a second packaged microelectronic device having a second array of external contacts different than the first array of external contacts, and wherein the test socket is configured to receive the second device; and a second mask proximate to the test socket and the test contacts, the second mask including a plurality of apertures arranged in a second pattern corresponding to the plurality of test contacts and corresponding at least in part to the second array of external contacts when the second device is received within the nesting portion, the plurality of apertures through the second mask including (a) third apertures configured to allow the corresponding test contacts to extend completely through the second mask, and (b) one or more fourth apertures configured to allow the corresponding test contacts to only extend partially through the second mask.
 15. A mask for use in a microelectronic device testing system, the testing system including a test socket, a microelectronic device having an array of external contacts carried by the test socket, and a tester interface including a plurality of test contacts configured to engage the external contacts, the mask comprising: a first surface facing the external contacts; a second surface opposite the first surface and facing the test contacts; and a plurality of apertures extending through the mask from the first surface to the second surface and positioned to receive the test contacts, the plurality of apertures including first apertures arranged in a pattern corresponding at least in part to the arrangement of external contacts on the device, the first apertures being sized to allow the corresponding test contacts to extend completely through the mask to the external contacts; and one or more second apertures sized to prevent the corresponding test contacts from extending completely through the mask.
 16. The mask of claim 15 wherein the test contacts each include a body portion, an engagement portion projecting from the body portion toward the external contacts, and a shoulder portion between the body portion and the engagement portion, the shoulder portion extending transversely with respect to the body portion and the engagement portion, and wherein: the first apertures have a first diameter sized to receive the body portion such that the engagement portions of the corresponding test contacts can extend completely through the mask; and the one or more second apertures have a second diameter less than the first diameter such that the shoulder portions of the test contacts aligned with the one or more second apertures engage the second surface of the mask and prevent the engagement portions of the corresponding test contacts from extending completely through the mask.
 17. The mask of claim 15 wherein the mask is a separate component configured to be releasably installed with the test socket before testing the device.
 18. The mask of 15 wherein the one or more second apertures are configured to electrically isolate the corresponding test contacts during testing of the device.
 19. The mask of claim 15, further comprising a conductive layer at the second surface of the mask and positioned to be electrically coupled to at least a portion of the test contacts aligned with the one or more second apertures.
 20. The mask of claim 15 wherein the plurality of apertures are arranged in rows and columns corresponding to the array of test contacts such that each test contact is at least partially received within an aperture.
 21. A system for testing a plurality of packaged microelectronic devices, the individual packaged devices including an array of external contacts , the system comprising: a test tray including a first test socket and a second test socket configured to receive corresponding packaged devices; a tester interface including a plurality of test contact arrays, the individual test contact arrays including a plurality of electrical interconnect elements aligned with the corresponding external contacts of the packaged devices when the packaged devices are received in the first and second test sockets; and a first mask proximate to the first test socket and a second mask proximate to the second test socket, the individual first and second masks including a plurality of apertures arranged in a pattern corresponding to the arrangement of interconnect elements in each test contact array with each interconnect element at least partially received within a corresponding aperture, the plurality of apertures in the first and second masks including (a) first apertures sized to allow the corresponding interconnect elements to extend completely through the associated first or second mask and engage the external contacts of the associated packaged device, and (b) second apertures sized to prevent the corresponding interconnect elements from engaging the associated packaged device by allowing such interconnect elements to only extend partially through the associated first or second mask, and wherein an arrangement of the first and second apertures in the first mask is different than an arrangement of the first and second apertures in the second mask.
 22. The system of claim 21 wherein: the individual first and second test sockets include a nesting portion carried by a base portion, the individual nesting portions including a body having one or more lead-in surfaces and a recess positioned to releasably receive the corresponding packaged devices; and the nesting portions are movable relative to the corresponding base portions between (a) a first position in which the interconnect elements are aligned with the corresponding first and second apertures and out of contact with the associated external contacts, and (b) a second position in which the interconnect elements aligned with the first apertures engage the corresponding external contacts of the associated packaged device and the interconnect elements aligned with the second apertures are out of contact with the associated packaged device.
 23. A system for testing a packaged microelectronic device including an array of external contacts, the system comprising: a test socket configured to releasably receive the device for testing; a tester interface including a plurality of test contacts aligned with external contacts of the device when the device is received within the test socket; and masking means proximate to the test socket for selectively allowing some test contacts to engage corresponding external contacts on the device while selectively restricting other test contacts from engaging the device.
 24. The system of claim 23 wherein the masking means includes a plurality of apertures arranged in a pattern corresponding at least in part to the array of external contacts when the device is received within the test socket, the plurality of apertures including (a) first apertures sized to allow the corresponding test contacts to extend completely through the masking means, and (b) one or more second apertures sized to allow the corresponding test contacts to extend only partially through the masking means.
 25. The system of claim 23 wherein: the individual test contacts include a body portion and a tip portion projecting from the body portion; the masking means includes a plurality of apertures arranged in a pattern corresponding at least in part to the array of external contacts when the device is received within the test socket, the apertures being positioned to allow a tip portion of some test contacts to touch the external contacts on the device while restricting other test contacts from contacting the device without making physical contact with a tip portion of the test contacts.
 26. The system of claim 23 wherein the masking means is an integral component of the test socket. 27-42. (canceled) 